Organic electroluminescent display device and method for fabricating the same

ABSTRACT

The present invention discloses organic electroluminescent display device and a method for fabricating the same, which includes: a first hole transporting layer formed in the first, second, and third pixel regions; a second hole transporting layer formed on a portion of the first hole transporting layer in the second and third pixel regions; a third hole transporting layer formed on a portion of the second hole transporting layer in the third pixel region. Light emitting layers are formed on each of the first, second, and third hole transporting layers. The thickness of the second hole transporting layer is approximately one-third (⅓) to two-thirds (⅔) of an optical wavelength difference between the first and second pixel regions, and the thickness of the third hole transporting layer is approximately one-third (⅓) to two-thirds (⅔) of an optical wavelength difference between the second and third pixel regions.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.11/185,850, filed Jul. 21, 2005, which claims the benefit of KoreanPatent Application No. 2004-57383, filed on Jul. 22, 2004, thedisclosure of which is hereby incorporated in its entirety by referenceherein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an organic electroluminescent displaydevice and a method of fabricating the same and, more particularly, toan organic electroluminescent display device having an optimum resonancestructure.

2. Description of the Related Art

An organic electroluminescent display (“OLED”) device having a thin filmtransistor (“TFT”) is a self light-emissive type display device, whichis attracting public attention as a next generation display devicebecause of its wide viewing angle, excellent contrast ratio, and fastresponse speed.

The OLED device is classified as either an inorganic electroluminescent(EL) device or an organic EL device depending on the material used toform a light emitting layer. Compared to the inorganic EL device, theorganic EL device may provide improved display performance in suchcharacteristics as luminance, driving voltage, response speed, and canalso provide a full-color display.

The OLED device has a full color feature because it may include a pixelcomprising pixel regions defined by the intersection of a plurality ofscan lines and a plurality of data lines, which can be arrangedsubstantially perpendicular to each other. Each pixel region correspondsto either red, green, or blue colors.

Referring to FIG. 1, a typical full-color OLED device has a substrate 10having a red pixel region (R), a green pixel region (G) and a blue pixelregion (B); and a plurality of first electrodes 12 formed on portions ofsubstrate 10 overlapping the red pixel region, the green pixel regionand the blue pixel region. In the case of a top-emission type OLEDdevice, the first electrode 12 can be a metal electrode, which may beeither a reflecting electrode or a transparent electrode containing areflecting layer.

In order to insulate the pixel regions and to define the pixel, aninsulating material layer is deposited and patterned to form a pixeldefining layer 14.

A hole injecting layer 16 and a hole transporting layer 18 are formedover the whole surface of substrate 10 to cover the first electrodes 12as a common layer.

A light emitting material layer is deposited on portions of holetransporting layer 18 that overlap the respective pixel regions tothereby form red (R), green (G) and blue (B) light emitting layers 20.

If needed, a hole blocking layer 21, an electron transporting layer 22,and an electron injecting layer 23 are sequentially formed over thewhole surface of substrate 10, and a second electrode layer 24 is formedon electron injecting layer 23. In a typical OLED, hole injecting layer16, hole transporting layer 18, light emitting layer 20, hole blockinglayer 21, electron transporting layer 22, and electron injecting layer23 are thin films made of an organic compound.

In a typical full-color OLED device, there is generally differences inluminous efficiency between respective pixel regions, i.e., therespective colors. For example, a green light emitting material has ahigher luminous efficiency than red and blue light emitting materials,and a red light emitting material has a higher luminous efficiency thana blue light emitting material.

As a result, much research has been performed to obtain maximum luminousefficiency and luminance by controlling the thickness of organic thinfilms. For example, Japanese Published Application No. 4-137485discloses a technique for improving luminous efficiency by forming theelectron transporting layer of a thickness between 30 to 60 nm on astructure that an anode, a hole transporting layer, a light emittinglayer, an electron transporting layer, and a cathode are sequentiallyformed.

Japanese Published Application No. 4-328295 discloses a technique ofsubstantially increasing luminance by controlling the thickness of theelectron transporting layer such that the light generated from the lightemitting layer interferes with the light reflected from the cathode.Also, Japanese Published Application No. 7-240277 discloses an OLEDdevice that controls an optical film thickness to improve luminance,particularly the color purity of blue light.

The OLED devices described above provide different optical filmthicknesses for each color to thereby improve luminance. However, it isvery difficult to form optical films of different thicknesses by usingdifferent manufacturing processes for each color.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an OLED device thathas optimum resonance structures for respective R, G and B pixel regionsand a method of fabricating the same.

The present invention discloses an organic electroluminescent displaydevice including: a substrate having first, second, and third pixelregions; a plurality of first electrodes formed on the substrate in eachof the first to third pixel regions; a hole injecting layer formed onthe substrate to cover the first electrodes; a first hole transportinglayer formed on the hole injection layer in the first, second, and thirdpixel regions; a second hole transporting layer formed on a portion ofthe first hole transporting layer in the second and third pixel regions;a third hole transporting layer formed on a portion of the second holetransporting layer in the third pixel region; first, second, and thirdlight emitting layers formed on the first, second, and third holetransporting layers, respectively; and a second electrode formed on thefirst, second, and third light emitting layers, wherein a thickness ofthe second hole transporting layer is one-third (⅓) to two-thirds (⅔) ofan optical wavelength difference between the first and second pixelregions, and a thickness of the third hole transporting layer isone-third (⅓) to two-thirds (⅔) of an optical wavelength differencebetween the second and third pixel regions.

The present invention further discloses an organic electroluminescentdisplay device including first, second, and third pixel regions, eachpixel region having a lower electrode and an organic light emittinglayer. The difference between a distance from the lower electrode to theorganic light emitting layer in one pixel region and a distance from thelower electrode to the organic light emitting layer in an adjacent pixelregion is one-third (⅓) to two-thirds (⅔) of an optical wavelengthdifference between the adjacent two pixel regions.

The present invention discloses a method for fabricating an organicelectroluminescent display device including: preparing a substrate;forming a plurality of first electrodes on the substrate; forming apixel defining layer on the substrate to cover the first electrodes;patterning the pixel defining layer to expose a light emitting region,thereby defining light emitting regions in each of a first, second, andthird pixel region; forming a hole injecting layer on the substrate;forming a first hole transporting layer on the hole injecting layer;forming a second hole transporting layer on the first hole transportinglayer in the second and third pixel regions; forming a third holetransporting layer on the second transporting layer in the third pixelregion; patterning first, second, and third light emitting materiallayers on the respective first, second, and third hole transportinglayers to form first, second, and third light emitting layers in therespective first, second, and third pixel regions; and forming a secondelectrode on the first, second, and third light emitting layers. Athickness of the second hole transporting layer is one-third (⅓) totwo-thirds (⅔) of an optical wavelength difference between the first andsecond pixel regions, and a thickness of the third hole transportinglayer is one-third (⅓) to two-thirds (⅔) of an optical wavelengthdifference between the second and third pixel regions.

In an alternative method for fabricating an organic electroluminescentdisplay device, the method includes forming the first hole transportinglayer and then forming the first light emitting material layer; formingthe second hole transporting layer and then forming the second lightemitting material layer; and forming the third transporting layer andthen forming the third light emitting material layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the present invention will become moreapparent to those of ordinary skill in the art when describing in detailembodiments thereof with reference to the attached drawings.

FIG. 1 is a cross-sectional view illustrating a typical full-color OLEDdevice.

FIG. 2 is a cross-sectional view illustrating an OLED device accordingto an embodiment of the present invention.

FIG. 3 is a cross-sectional view illustrating an OLED device accordingto another embodiment of the present invention.

FIGS. 4 and 5 are graphs an efficiency and a color coordinate of a redcolor OLED device according to first embodiment of the presentinvention.

FIGS. 6 and 7 are graphs an efficiency and a color coordinate of a greencolor OLED device according to second embodiment of the presentinvention.

FIG. 8 is a graph of power consumption of a blue color OLED deviceaccording to third embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which embodiments of theinvention are shown. This invention may, however, be embodied indifferent forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art.

In the drawings, the thickness of layers and regions are exaggerated forclarity. It will be understood that when an element such as a layer,film, region or substrate is referred to as being “on” another element,it can be directly on the other element or intervening elements may alsobe present. In contrast, when an element is referred to as being“directly on” another element, there are no intervening elementspresent. Like numbers refer to like elements throughout thespecification.

Referring to FIG. 2, the OLED device of the present invention mayinclude: a substrate 210 having a first pixel region 100, a second pixelregion 200, and a third pixel region 300; and a plurality of firstelectrodes 212 formed on portions of the substrate 210 in each of pixelregions 100, 200, 300.

Pixel regions 100, 200, 300 implement different colors, which maycorrespond to red, green, or blue. For example, assuming that firstpixel region 100 is red and second pixel region 200 is green, then thirdpixel region 300 is blue. Further, assuming that first pixel region 100is green and second pixel region 200 is blue, then third pixel region300 is red.

Preferably, first pixel region 100 is blue, the second pixel region 200is green, and the third pixel region 300 is red. But the invention isnot limited to such an arrangement of the pixel regions that comprise apixel.

A transparent insulating substrate such as a glass substrate or aplastic substrate may be used for substrate 210.

The plurality of first electrodes 212 may be reflecting electrodes. Thereflecting electrode can be made from a group comprising aluminum (Al),aluminum alloy, a dual-layered reflecting anode which contains indiumtin oxide (ITO) or indium zinc oxide (IZO) and silver (Ag), and atriple-layered electrode that contains Ag and ITO.

Subsequently, a pixel defining layer 214 is deposited on firstelectrodes 212. Pixel defining layer 214 is patterned to include anopening portion corresponding to a light emitting region. Pixel defininglayer 214 may be formed of an organic insulating layer such asbenzo-cylo-butene (BCB) or acrylic resin.

Then, a hole injecting layer 216 is formed on first electrode layer 212.Hole injecting layer 216 may be formed over the whole surface ofsubstrate 210 as a common layer to cover the respective pixel regions100, 200, 300. Hole injecting layer 216 may be made of a typical holeinjecting layer material such as copper phthalocyanine (CuPc) or4,4′,4″-tris(N-3-methylphenyl-N-phenylamino)-triphenylamine (mTDATA).

A first hole transporting layer 218-1 is formed over the whole surfaceof substrate 210 to cover hole injecting layer 216. First holetransporting layer 218-1 may be formed as a common layer. First holetransporting layer 218-1 may have a thickness between 300-500 Å or thetotal thickness of both hole injecting layer 216 and first holetransporting layer 218-1 may be between 1,300-1,500 Å.

A second hole transporting layer 218-2 is formed using a fine metal maskon portions of the first hole transporting layer 18-1 overlapping secondand third pixel regions 200, 300.

A third hole transporting layer 218-3 is formed again using a fine metalmask on a portion of the first hole transporting layer 218-1 overlappingthird pixel region 300. As a result, hole transporting layer 218 isformed having portions of different thicknesses overlapping each of thepixel regions 100, 200, 300.

Red, green, and blue light have different wavelengths at maximumintensity. For example, at maximum intensity, blue light has awavelength of approximately 460 nm, green light has a wavelength ofapproximately 520 nm, and red light has a wavelength of approximately630 nm. At this time, if both an optical path (e.g., “a” in first pixelregion 100) and an optical thickness (e.g., “a/2” in first pixel region100) between first electrode 12 and the light emitting layer 20 areidentical for the respective colors but there is a difference in amoving distance of light according to the wavelength for each color,optimum optical characteristics cannot be obtained.

Therefore, by providing differing optical thicknesses between a firstelectrode and a light emitting layer for each color to account forwavelength differences between the respective colors at a maximumintensity, an optimum optical resonance structure can be obtained.

To achieve an optimum optical resonance structure, a difference betweenoptical paths (i.e., optical thicknesses) between first electrodes 212and light emitting layers 220-1, 220-2 in the adjacent two pixel regions100, 200 is set to one-third (⅓) to two-thirds (⅔) of the wavelengthdifference of the colors at maximum intensity for each pixel region. InFIG. 2, the differences in optical paths between pixel regions 100, 200is set at one-half (½) the wavelength difference at maximum intensity

For example, as shown in FIG. 2, assuming that a difference between thewavelengths of the colors at maximum intensity for the first and secondpixel regions 100, 200 is 2x, then a difference between the optical pathfrom first electrode 212 to light emitting layer 220-1 in first pixelregion 100 and an optical path from first electrode 212 to lightemitting layer 220-2 in second pixel region 200 is set to 2x. Thus, ifthe optical path of the first pixel region 100 is “a”, then the opticalpath of the second pixel region 200 is set to “a+2x.” Therefore, adifference between the optical thickness of first pixel region 100 andsecond pixel region 200 becomes “x” to provide the optical path “a+2x”in second pixel region 200.

Accordingly, if the thickness second hole transporting layer 218-2 isset to “x”, the optimum optical resonance structure can be obtained. Thevalue of “x” may be between 300-500 Å or the total thickness of bothhole injecting layer 216 and the first and second hole transportinglayers 218-1, 218-2 may be between 1,300-1,500 Å.

Further, assuming that a difference between a wavelengths of the colorsat maximum intensity for the second and third pixel regions 200, 300 is2y, then a difference between the optical path from first electrode 212to light emitting layer 220-2 in second pixel region 200 and an opticalpath from first electrode 212 to light emitting layer 220-3 in thirdpixel region 300 is 2y. Thus, if third transporting layer 218-3 isformed at the thickness of “y” to provide the optical path “a+2x+2y” inthird pixel region 300, then the optimum optical resonance structure canbe obtained. The value of “y” may be between 300 Å-500 Å or the totalthickness of the hole injecting layer 216 and first, second, and thirdhole transporting layers 218-1, 218-2, 218-3 may be between 2,100-2,300Å.

The embodiment described above illustrated an optical thicknessdifference of one-half (½) the wavelength difference of the colors atmaximum intensity for adjacent pixel regions, but the OLED device havingthe optimum resonance structure can be manufactured using a varyingthicknesses from approximately one-third (⅓) to two thirds (⅔) of thiswavelength difference.

Second and third hole transporting layers 218-2, 218-3 can be formed onthe respective pixel regions 200, 300 separately, but to simplify themanufacturing process second transporting layer 218-2 may be formed as acommon layer overlapping both second and third pixel regions 200, 300.

Here, first, second, and third hole transporting layers 218-1, 218-2,218-3 may be made of N,N′-di(1-naphthyl)-N,N′-diphenyl-benzidene (NPD)or polyethylenethioxythiophene (PEDOT). In addition, each holetransporting layer 218-1, 218-2, 218-3 may be made of differentmaterials from one another.

The thickness of first hole transporting layer 218-1 is set to satisfythe device characteristics for the respective pixel regions. Using blueas an example, if hole injecting layer 216 has thickness of 1,000 Å,then the thickness of first hole transporting layer 218-1 may be 300-500Å. Since the optimum efficiency of blue light is at a wavelength ofapproximately 460 nm, i.e., 4,600 Å, an optimum efficiency can beobtained, due to constructive interference, when the total thickness ofhole injecting layer 216 and hole transporting layer 218-1 is around1,300 Å, which in consideration of the optical path is closest toone-half the wavelength of blue light.

First, second, and third light emitting material layers may be depositedon hole transporting layer 218 and then patterned to form respectivefirst, second, and third light emitting layers 220-1, 220-2, 220-3. Inthe described embodiment, first, second, and third pixel regions 100,200, 300 correspond to red, green and blue colors to implement thefull-color OLED device. However, if device characteristics such asluminous efficiency are considered, the red pixel region may have thethickest hole transporting layer because red has the longest wavelength,the green pixel may have the next thickest hole transporting layerbecause green has the next longest wavelength, and blue subpixel mayhave the least thick hole transporting layer because blue has theshortest wavelength.

Therefore, for achieving optimal luminous efficiency, a blue lightemitting layer 220-1 may be formed in first pixel region 100, a greenlight emitting layer 220-2 may be formed in second pixel region 200, anda red light emitting layer 220-3 may be formed in third pixel region300.

The red light emitting layer contains carbazole biphenyl (CBP) or1,3-dicarbazole-benzene (mCP) as a host material and a phosphorescentmaterial which contains at least one dopant material selected from agroup comprised ofPQIr(acac)(bis(1-phenylquinoline)-acetylacetonate-iridium), PQIr(tris(1-phenylquinoline) iridium), and PtOEP(platinum-octaethylporphyrin). Also, the red light emitting layer may bemade of a fluorescent material such as Eu(DBM)₃(Phen):PBD or Perylene.

The green light emitting layer contains CBP or mCP as a host materialand contains a phosphorescent material which contains Ir(ppy)₃ (factris(2-phenylpyridine)iridium) as a dopant material. The green lightemitting layer may be made of a fluorescent material such as Alq₃(aluminum-tris(8-hydroxyquinolino)).

The blue light emitting layer is made of a fluorescent material whichmay contain one of the following: DPVBi, spiro-DPVBi, spiro-6P,distyrylbenzene (DSB), distyrylarylene (DSA), PFO-based polymer, andPPV-based polymer. The blue light emitting layer can be made from one ofthe fluorescent materials listed above instead of a phosphorescentmaterial to improve the stability of optical characteristics.

The light emitting layer may be formed using known techniques such as alaser induced thermal imaging (LITI), an ink jet method, a vacuumdeposition method, or any other suitable technique for forming such alayer.

Second electrode layer 24 may be formed of a transmissive metalelectrode such as Ca, Ca/Ag, or Mg/Ag.

The OLED device of the present invention may further include at leastone of the following: hole blocking layer 221, electron transportinglayer 222, and electron injecting layer 223.

Hole blocking layer 221 may be made ofbis(2-methyl-8-quinolinolate)-(4-hydroxy-biphenylyl)-aluminum (BAlq);hole transporting layer 22 may be made of polycyclic hydrocarbon-likederivative, heterocyclic compound, or tris(8-quinolitorato)-aluminum(Alq₃); and electron injecting layer 23 may be made of LiF, Liq, NaF orNaq.

Moreover, a passivation layer (not shown) may further be formed onsecond electrode layer 24. The passivation layer may be made of SiNx orSiO₂.

Referring to FIG. 3, the OLED device according to another embodiment ofthe present invention is arranged in as similar manner as the OLEDillustrated in FIG. 2.

Unlike the previous embodiment, however, the hole transporting layers ofdifferent thicknesses are formed individually in each pixel region. Forexample, a first hole transporting layer 318-1 is formed on the portionof hole injecting layer 216 disposed in only first pixel region 100.

Subsequently, a second hole transporting layer 318-2 is formed only insecond pixel region 200, and thereafter a third hole transporting layer318-3 is formed only in third pixel region 300.

In the previous embodiment, the hole transporting layer 218 is formed ofoverlapping multiple layers 218-1, 218-2, 218-3, but the holetransporting layer of another embodiment of the present invention isformed such that one layer 318-1, 318-2, 318-3 is formed in each of thepixel regions 100, 200, 300, respectively.

As in the previous embodiment, the first, second, and third holetransporting layers may be made of different materials from one another.

Also, after depositing the hole transporting layers 318-1, 318-2, 318-3,red, green, and blue light emitting materials may be deposited using afine metal mask to form light emitting layers 220-1, 220-2, 220-3.Alternatively, each light emitting layer may be deposited directly afterits corresponding hole transporting layer is deposited. For example, ablue light emitting layer 220-1 may be deposited using a fine metal maskdirectly after depositing first hole transporting layer 318-1, a greenlight emitting layer 220-2 may be deposited directly after depositingsecond hole transporting layer 318-2, and then a red light emittinglayer 220-3 may be deposited directly after depositing third holetransporting layer 318-3.

The below manufacturing examples are to describe a method formanufacturing an OELD device with red, green and blue light emittinglayers according to the present invention.

Manufacturing Example R1

A reflective pixel electrode is prepared such that a substrate (aluminumand ITO)(available from SDI company) having a thickness of 1,300 Å iscut to have a size of 50 mm×50 mm×0.7 mm, is ultrasonic-cleaned inIsopropyl alcohol and pure water during five minutes respectively andthen is ultraviolet and ozone-cleaned during thirty minutes.

A hole injecting layer having a thickness of 1,000 Å is formed on thepixel electrode by using m-TDATA which is a hole injecting material, anda hole transporting layer having a thickness of 1,200 Å is formed on thehole injecting layer using a NPB which is a hole transporting material.

A red light emitting layer having a thickness of 300 Å is formed on thehole transporting layer using CBP and BPTIr as a red light emittingmaterial, and a hole blocking layer having a thickness of 50 Å is formedby depositing Balq on the red light emitting layer. Alq3 is deposited ata thickness of 250 Å on the hole blocking layer to form an electrontransporting layer, and Lif is deposited at a thickness of 3 Å on theelectron transporting layer to form an electron injecting layer.Finally, a transparent opposite electrode is formed at a thickness of180 Å using MgAg, thereby manufacturing the OELD device. The OELD devicemanufactured by the manufacturing example R1 is referred to as SampleR1.

Manufacturing Example R2

A manufacturing method of the manufacturing example R2 is the same asthat of the manufacturing example R1 except that the hole transportinglayer is formed at a thickness of 1,000 Å. The OELD device manufacturedby the manufacturing example R2 is referred to as Sample R2.

Manufacturing Example R3

A manufacturing method of the manufacturing example R3 is the same asthat of the manufacturing example R1 except that the hole transportinglayer is formed at a thickness of 1,400 Å. The OELD device manufacturedby the manufacturing example R3 is referred to as Sample R3.

Manufacturing Example R

A manufacturing method of the manufacturing example R is the same asthat of the manufacturing example R1 except that the hole transportinglayer is formed at a thickness of 800 Å. The OELD device manufactured bythe manufacturing example R2 is referred to as Sample R.

Manufacturing Example G1

A manufacturing method of the manufacturing example G1 is the same asthat of the manufacturing example R1 except that NPB as a holetransporting material is deposited at a thickness 800 Å to form the holetransporting layer and CBP and Irppy as a green light emitting materialare deposited at 300 Å to form a green light emitting layer instead ofthe red light emitting layer. The OELD device manufactured by themanufacturing example G1 is referred to as Sample G1.

Manufacturing Example G2

A manufacturing method of the manufacturing example G2 is the same asthat of the manufacturing example G1 except that the hole transportinglayer is formed at a thickness of 600 Å. The OELD device manufactured bythe manufacturing example G2 is referred to as Sample G2.

Manufacturing Example G3

A manufacturing method of the manufacturing example G3 is the same asthat of the manufacturing example G1 except that the hole transportinglayer is formed at a thickness of 900 Å. The OELD device manufactured bythe manufacturing example G3 is referred to as Sample G3.

Manufacturing Example G

A manufacturing method of the manufacturing example G is the same asthat of the manufacturing example G1 except that the hole transportinglayer is formed at a thickness of 500 Å. The OELD device manufactured bythe manufacturing example G is referred to as Sample G.

Manufacturing Example B1

A manufacturing method of the manufacturing example B1 is the same asthat of the manufacturing example R1 except that NPB as a holetransporting material is deposited at a thickness 400 Å to form the holetransporting layer and IDE140 (available from Idemistu company) andIDE105 (available from Idemistu company) as a blue light emittingmaterial is deposited at 150 Å to form a blue light emitting layerinstead of the red light emitting layer. The OELD device manufactured bythe manufacturing example B1 is referred to as Sample B1.

Manufacturing Example B2

A manufacturing method of the manufacturing example B2 is the same asthat of the manufacturing example B1 except that the hole transportinglayer is formed at a thickness of 300 Å. The OELD device manufactured bythe manufacturing example B2 is referred to as Sample B2.

Manufacturing Example B3

A manufacturing method of the manufacturing example B3 is the same asthat of the manufacturing example B1 except that the hole transportinglayer is formed at a thickness of 500 Å. The OELD device manufactured bythe manufacturing example B3 is referred to as Sample B3.

Manufacturing Example B

A manufacturing method of the manufacturing example B is the same asthat of the manufacturing example B1 except that the hole transportinglayer is formed at a thickness of 200 Å. The OELD device manufactured bythe manufacturing example B is referred to as Sample B.

Evaluation Example 1 Evaluation of Efficiency, a Color Coordinate andPower on Samples Obtained from the Above-Described ManufacturingExamples

Performance of the samples described above has been evaluated.Efficiency and a color coordinate on Samples R1, R2, R3, and R andSamples G1, G2, G3, and G have been evaluated and are shown in FIGS. 4to 7. Efficiency and color purity have been measured using the IVLmeasuring device (PhotoResearch PR650, Keithley 238).

Performance of Samples B1, B2, B3, and B has been evaluated by measuringpower consumption of respective samples, and the result is shown in FIG.8. In case of blue color emission, the color coordinate variationsensitively affects the whole power consumption and thus has beenevaluated using power consumption measured in consideration of both thecoordinate and efficiency. The power consumption has been calculatedafter evaluating the efficiency and the color purity using the IVLmeasuring device (PhotoResearch PR650, Keithley 238).

In FIGS. 4 to 8, an x-axis denotes a thickness of the hole transportinglayer of respective samples.

FIG. 4 is a graph illustrating efficiencies of Samples R1, R2, R3, andR. As shown in FIG. 7, the efficiency of Sample R does not reach even 1,but the efficiency of Sample R1 is more than 6, and thus it can beunderstood that Sample R1 has very high efficiency.

FIG. 5 is a graph illustrating color coordinates of Samples R1, R2, R3,and R. Since a NTSC level of the red is (0.67, 0.32), the colorcoordinate of Sample R is (0.635, 0.36) which does not reach the redNTSC level, but the color coordinate of Sample R1 is (0.672, 0.32), andthus it can be understood that Sample R1 has very excellent colorcoordinate.

FIG. 6 is a graph illustrating efficiencies of Samples G1, G2, G3, andG.

As shown in FIG. 9, the efficiency of Sample G is just 5, but theefficiency of Sample G1 is about 25 which is five times as high as thatof Sample 5, and thus it can be understood that Sample G1 has very highefficiency.

FIG. 7 is a graph illustrating color coordinates of Samples G1, G2, G3,and G. Since a NTSC level of the green is (0.21, 0.71), the colorcoordinate of Sample G is (0.14, 0.65) which does not reach the red NTSClevel, but the color coordinate of Sample G1 is (0.21, 0.726), and thusit can be understood that Sample G1 has very excellent color coordinate.

FIG. 8 is a graph illustrating power consumption of Samples B1, B2, B3,and B. As shown in FIG. 8, Sample B has power consumption of 570 mWwhich is very high, but Sample B1 has just power consumption of about400 mW, and thus it can be understood that Sample B1 has very excellentpower consumption.

Embodiment 1

This embodiment describes a method for manufacturing an OELD devicewhich has all of red, green and blue light emitting layers as an OELDdevice which is optimized in thickness of the hole injecting layer andthe hole transporting layer.

A substrate having a thin film transistor (TFT) is prepared, and a pixelelectrode made of aluminum is formed at a thickness 1,000 Å in the formof stripe. Here, the pixel electrode is formed to be electricallyconnected to source and drain electrodes of the TFT arranged on thelower substrate.

A pixel defining layer which defines regions on which red, green andblue light emitting layers are to be formed is formed on the pixelelectrode using a silicon oxide material. Then, m-TDATA as a holeinjecting material is deposited at a thickness of 1,000 Å to form thehole injecting layer. NPB as a hole transporting material is depositedat a thickness of 400 Å to form the hole transporting layer. Using aphoto mask, NPB is additionally deposited at a thickness of 400 Å on theregion on which the green light emitting layer is to be formed, and NPBis additionally deposited at a thickness of 800 Å on the region on whichthe red light emitting layer is to be formed, so that a thickness of thehole transporting layer corresponding the red light emitting region is1,200 Å, a thickness of the hole transporting layer corresponding thegreen light emitting region is 800 Å, and a thickness of the holetransporting layer corresponding the blue light emitting region is 400Å.

On the hole transporting layer, CBP and BTPIr as a red light emittingmaterial are formed at a thickness of 300 Å, CBP and Irppy as a greenlight emitting material are formed at a thickness of 300 Å, and IDE140(available from Idemistu company) and IDE105 (available from Idemistucompany) as a blue light emitting material are formed at a thickness of150 Å.

Balq is deposited on the light emitting layer to form the hole blockinglayer of a thickness of 50 Å. Alq3 is formed on the hole blocking layerat a thickness of 250 Å to form the electron transporting layer, and LiFis formed on the electron transporting layer at a thickness of 3 Å.Then, Mg:Ag is formed at a thickness of 180 Å as the transparentopposite electrode, whereby manufacturing the OELD device.

Evaluation 2 Performance Evaluation of OELD Device of Embodiment 1

Voltage, current, luminance, efficiency, and color coordinate of theOELD device manufactured by Embodiment 1 have been evaluated by the samemethod of Evaluation Example 1. The result is shown in Table 1.

TABLE 1 Voltage Current luminance Efficieny x color y color (V) (mA/cm2)(cd/m2) (cd/A) coordinate coordinate Red light emitting layer 8.17 37.192000 5.39 0.67 0.32 Green light emitting layer 6.56 16.40 4000 24.450.21 0.72 Blue light emitting layer 6.36 42.92 600 1.40 0.14 0.06

As can be seen Table 1, the OELD device of Embodiment 1 is excellent inluminance, efficiency and color coordinate for respective color lightemitting layers.

Embodiment 2

This embodiment describes a method for manufacturing a flat paneldisplay device which has two or more OELD devices to display throughboth sides.

A transparent substrate which has first and second display regions and athin film transistor is prepared. A first OELD device is formed on thefirst display region of the substrate in the same way as Embodiment 1. Asecond OELD device which has layered structure of Table 2 below isformed on a surface corresponding to the surface on which the first OELDdevice is formed, thereby manufacturing the flat panel display devicewhich can display through both sides. That is, the first OELD device isa front light emitting type which has a reflective pixel electrode and atransparent opposite electrode, whereas the second OELD device is abottom light emitting type which has a transparent pixel electrode and areflective opposite electrode.

TABLE 2 Red light Green light Blue light emitting region emitting regionemitting region Pixel electrode ITO 1500 Å ITO 1500 Å ITO 1500 Å Holetransporting layer NPB (500 Å) NPB (500 Å) NPB (500 Å) Light emittinglayer host CBP (300 Å) CBP (300 Å) IDE140 (200 Å) Light emitting layerdopant BTPIr (10 weight %) Ir (ppy) 3 (5 weight %) IDE105 (5 weight %)Hole blocking layer Balq (50 Å) Balq (50 Å) Balq (50 Å) Electrontransporting layer Alq3 (200 Å) Alq3 (200 Å) Alq3 (200 Å) Electroninjecting layer LiF (10 Å) LiF (10 Å) LiF (10 Å) Opposite electrode Al(3000 Å) Al (3000 Å) Al (3000 Å)

Evaluation Example 3 Performance Evaluation of Flat Panel Display Deviceof Embodiment 2

Voltage, current, luminance, efficiency, and color coordinate of thefirst and second OELD devices of the flat panel display device ofEmbodiments have been evaluated by the same method of EvaluationExample 1. Performance evaluation result of the first OELD device is thesame as that of Table 1, and performance evaluation result of the secondOELD device is shown in Table 3.

TABLE 3 Voltage Current Luminance Efficiency x color y color (V)(mA/cm²) (cd/m²) (cd/A) coordinate coordinate Red light emitting layer6.803 12.779 600 4.712 0.677 0.320 Green light emitting layer 6.6413.516 1000 28.518 0.316 0.619 Blue light emitting layer 6.142 14.020 7004.986 0.148 0.152

As can be seen in Tables 2 and 3, the flat panel display device whichcan display through both sides has excellent performance.

As described herein, according to the present invention, the holetransporting layer may have different thicknesses according to the colorimplemented by each pixel region, and, thus, provides a full-color OLEDdevice with an optimum resonance structure.

1. An organic electroluminescent display device, comprising: a firstpixel region having a first lower electrode and a first organic lightemitting layer; a second pixel region having a second lower electrodeand a second organic light emitting layer; and a third pixel regionhaving a third lower electrode and a third organic light emitting layer,wherein a difference between a distance from the lower electrode to theorganic light emitting layer of one pixel region and a distance from thelower electrode to the organic light emitting layer of an adjacent pixelregion is approximately one-third (⅓) to two-thirds (⅔) of an opticalwavelength difference between the two adjacent pixel regions.
 2. Thedevice of claim 1, wherein the difference between distance from thelower electrode to the organic light emitting layer of one pixel regionand the distance from the lower electrode to the organic light emittinglayer of an adjacent pixel region pixel region is approximately one-half(½) to two-thirds (⅔) of an optical wavelength difference between thetwo adjacent pixel regions.
 3. The device of claim 1, wherein the first,second, and third pixel regions implement different colors, whichcorrespond to red, green or blue.
 4. The device of claim 3, wherein thefirst pixel region corresponds to blue, the second pixel regioncorresponds to green, and the third pixel region corresponds to red. 5.The device of claim 4, wherein the second pixel region is adjacent tothe first pixel region, and the third pixel region is adjacent to thesecond pixel region.
 6. The device of claim 5, wherein a differencebetween the distance from the first lower electrode to the first organiclight emitting later and the distance from the second lower electrode tothe second organic light emitting layer is between approximately 300 Åand 500 Å.
 7. The device of claim 5, wherein a difference between thedistance from the second lower electrode to the second organic lightemitting later and the distance from the third lower electrode to thethird organic light emitting layer is between approximately 300 Å and500 Å.
 8. The device of claim 5, further comprising: a hole injectinglayer formed on the lower electrodes; and a hole transporting layerbetween the lower electrodes and the organic light emitting layers. 9.The device of claim 8, wherein the hole injecting layer is formed as acommon layer in the first, second, and third pixel regions.
 10. Thedevice of claim 8, wherein the hole transporting layer has a differentthickness in each of the first, second, and third pixel regions.
 11. Thedevice of claim 10, wherein the thickness of the hole transporting layeris in the third pixel region is greater than the thickness of the holetransporting layer in the second pixel region, and the thickness of thehole transporting layer in the second pixel region is greater than thethickness of the hole transporting layer in the first pixel region. 12.The device of claim 10, wherein a difference between the thickness of aportion of the hole transporting layer in the first pixel region and thethickness of a portion of the hole transporting layer in the secondpixel region is between approximately 300 Å and 500 Å.
 13. The device ofclaim 10, wherein a difference between the thickness of a portion of thehole transporting layer in the second pixel region and the thickness ofa portion of the hole transporting layer in the third pixel region isbetween approximately 300 Å and 500 Å.
 14. The device of claim 11,wherein a portion of the hole transporting layer in the second pixelregion has a dual-layered structure, and a portion of the holetransporting layer in the third pixel region has a triple-layeredstructure.